C# — should we should cast for get in Indexer Method

Question

public class PeopleCollection : IEnumerable
{
    private Dictionary<string, Person> listPeople = new Dictionary<string, Person>();

    // This indexer returns a person based on a string index.
    public Person this[string name]
    {
        get { 
            return (Person)listPeople[name]; // **Is this cast necessary?**
        }
        set { 
            listPeople[name] = value; 
        }
    }
    ..
}

Question: should we cast the return value from listPeople[name] to Person ?

Thank you

Answer 1

No, it is not needed. In Dictionary<TKey, TValue> the indexer is declared as:

public TValue this[TKey key] { get; set; }

For the Dictionary<string, Person> in the listPeople field, TValue is replaced with Person , so the indexer will return a reference to a Person object.

Answer 2

No, that cast isn't necessary. Dictionary's indexer is already strongly typed to return Person (because that's what TValue is for that dictionary). That's one of the benefits of generics :)

Of course, the simplest way to find this out would be to remove the cast and see - if the Dictionary indexer hadn't been strongly typed, your code would have failed to compile as you'd have been trying to return object (or whatever) for an indexer of type Person .

Answer 3

不需要，但这不是必须的，但是如果您删除了（Person）并对其进行了编译，您将会发现。